When functioning properly, the human heart maintains its own intrinsic rhythm and will pump an adequate supply of blood throughout the body's circulatory system. However, some people have cardiac arrhythmias that result in diminished blood circulation. One method of treating cardiac arrhythmias is the administration of drug therapy. Another method is the use of a cardiac rhythm management system. Such systems (pacers, cardioverters, among others) are usually implanted in the patient and deliver electrical stimulation therapy directly to the heart.
One type of cardiac disturbance faced by cardiac rhythm management systems is congestive heart failure (CHF). CHF, which can result from long-term hypertension, is a condition in which the muscles in the walls of the right and/or left sides of the heart are stretched abnormally with each cardiac filling and contraction. As a result, the left atrium and left ventricle become enlarged, and the heart muscle possesses less contractility, a condition called left ventricular dysfunction (LVD). LVD decreases cardiac output, which, in turn, often results in an increased heart rate with less resting time between contractions. The heart consumes more oxygen, and its condition, along with the patient's, typically worsens over a period of time.
When the left side of the heart has become enlarged due to CHF, the ventricular depolarization signals may travel through and depolarize the left side of the heart more slowly than they do in the right ventricle. As a result, the left and right ventricles do not contract simultaneously. Rather, the left ventricle contracts somewhat later than the right ventricle. This further reduces the pumping efficiency of the heart. Furthermore, significant conduction disturbances between the right and left atria can result in left atrial flutter or fibrillation, further reducing the pumping efficiency of the heart.
As a result, there has been a need to provide CHF patients with a pacing therapy that coordinates ventricular contractions or otherwise increases the heart's pumping efficiency. Most recently, biventricular synchronous pacing that provides pacing pulses to both right and left ventricles has met this need.
In general, conduction disturbances in LVD patients benefit from pacing pulses applied at multiple electrode sites positioned in or about a single heart chamber or in both right and left heart chambers. These pacing pulses may also be delivered in synchrony with paced or sensed depolarizations detected at one of the electrode sites. Atrial and left ventricular cardiac output can be significantly improved when left and right chamber synchrony is restored, particularly in patients suffering from dilated cardiomyopathy, LVD and CHF.
A number of proposals have been advanced for providing pacing therapies to restore synchronous depolarization and contraction of a single heart chamber and the like as described in detail in the commonly assigned U.S. Pat. No. 6,129,744 and in commonly assigned U.S. Pat. Nos. 5,626,623, 5,403,356, 5,797,970, 5,902,324, and 6,070,100 and in U.S. Pat. Nos. 5,720,768 and 5,792,203 the contents of each patent is hereby incorporated by reference herein. The proposals appearing in U.S. Pat. Nos. 3,937,226, 4,088,140, 4,548,203, 4,458,677, 4,332,259 are summarized in U.S. Pat. Nos. 4,928,688 and 5,674,259. The advantages of providing sensing at pace/sense electrodes located in both the right and left heart chambers is addressed in the '688 and '259 patents, as well as in U.S. Pat. Nos. 4,354,497, 5,174,289, 5,267,560, 5,514,161, and 5,584,867. The art has recently turned its attention to the duration of A-V and/or V-V intervals to improve biventricular pacing. In U.S. Pat. No. 6,144,880, to Ding et al. purportedly describe multiple ways to provide optimized timing for ventricular pacing by determining certain intrinsic electrical or mechanical events in the atria or ventricles that have a predictable timing relationship to the delivery of optimally timed ventricular pacing that maximizes ventricular performance. This patent purportedly discloses methods to predict AV intervals for use in biventricular pacing based on numerous tests and experiments to measure hemodynamic parameters, from which generic algorithms were developed that are applied to all patients. These measurements, as the inventors make quite clear, do not use patient-specific measurements of hemodynamic parameters. In U.S. Pat. No. 6,285,907, Kramer et al. purportedly disclose techniques for computing an AV interval in biventricular pacing based on an underlying intrinsic heart rate, the intrinsic AV interval, or sensor indicated rate. The methods proposed in this patent, while they are patient-specific, are not directly derived from the measurement of hemodynamic parameters.
In U.S. Pat. No. 6,804,555 to Warkentin a system and method for monitoring the QRS duration is provided wherein processing QRS duration signals provides data from which the onset or progression of heart failure is determined. In the Warkentin patent, adjusting SAV/PAV delays and/or V-V delays provides a way to improve delivery of synchronous pacing pulses as a function of QRS duration. The SAV/PAV/V-V delays are varied from the prevailing delays as a function of the measured width of the QRS complex. The Warkentin patent was filed 29 Jun. 2001 and is entitled, “Multi-site Venticular Pacing System Measuring QRS Duration,” is hereby incorporated by reference herein.
The medical literature also discloses a number of approaches for providing bi-atrial and/or bi-ventricular pacing as set forth in: Daubert et al., “Permanent Dual Atrium Pacing in Major Intra-atrial Conduction Blocks: A Four Years Experience”, PACE (Vol. 16, Part II, NASPE Abstract 141, p.885, April 1993); Daubert et al., “Permanent Left Ventricular Pacing With Transvenous Leads Inserted Into The Coronary Veins”, PACE (Vol. 21, Part II, pp. 239–245, January 1998); Cazeau et al., “Four Chamber Pacing in Dilated Cardiomyopathy”, PACE (Vol. 17, Part II, pp. 1974–1979, November 1994); and Daubert et al., “Renewal of Permanent Left Atrial Pacing via the Coronary Sinus”, PACE (Vol. 15, Part II, NASPE Abstract 255, p. 572, April 1992).
Kass et al., in “Improved Left Ventricular Mechanics From Acute VDD Pacing in Patients With Dilated Cardiomyopathy and Ventricular Conduction Delay,” Circulation, (Mar. 30, 1999), report the results of their study of the impact of dP/dtmax, arterial pulse pressure (PP), and peak-systolic pressure measurements at various pacing sites in VDD pacing, with data at optimized A-V intervals for each site in the tested patients.
With respect to pressure sensing apparatus capable of chronic in vivo operation, many devices and methodologies have been proposed and/or implemented in the prior art. In this regard, the following issued U.S. patents provide added details for several representative pressure monitoring techniques; namely: U.S. Pat. Nos. 5,368,040; 5,564,434; 6,171,252; and 6,221,024 the contents of each are hereby incorporated herein as if fully set forth herein.